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Related Concept Videos

Functional Classification of Joints01:09

Functional Classification of Joints

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Functional Classification of Joints
The functional classification of joints is determined by the amount of mobility between the adjacent bones. Joints are functionally classified as a synarthrosis or immobile joint, an amphiarthrosis or slightly moveable joint, or as a diarthrosis, a freely moveable joint. Fibrous and cartilaginous joints can be functionally classified as either synarthroses  or amphiarthroses, whereas all synovial joints are classified as diarthroses.
Synarthrosis
An...
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Body Planes01:06

Body Planes

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Body planes in anatomy are imaginary flat surfaces used as reference points to divide the body into sections for anatomical study. These planes are essential for understanding the orientation, relationships, and spatial organization of anatomical structures.
The sagittal plane is the plane that divides the body or an organ vertically into right and left sides. If this vertical plane runs directly down the middle of the body resulting in equal division, it is called the midsagittal or median...
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Knee Joint01:23

Knee Joint

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The knee joint is the most complicated joint in the body. It consists of three articulations– two tibiofemoral and one patellofemoral. As is characteristic of synovial joints, the knee joint has a thin articular capsule that partially surrounds this joint cavity. Additionally, several ligaments, muscles, and cartilaginous structures support the movement of the knee.
A total of seven ligaments support the knee joint. The patellar ligament, which is also attached to the quadriceps femoris...
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Bones of the Lower Limb: Femur and Patella01:16

Bones of the Lower Limb: Femur and Patella

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The femur is the body's longest and strongest bone spanning the thigh region. Its head articulates with the acetabulum of the hip bone to form the hip joint. A minor indentation on the medial side of the femoral head, called the fovea capitis, serves as the site of attachment for the ligament of the head of the femur. This weak ligament spans the femur and acetabulum and supports the hip joint. The narrowed region below the head is the neck of the femur. The inclination angle between the...
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Structural Classification of Joints01:20

Structural Classification of Joints

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Joints, also known as articulations, are classified based on their structural characteristics, i.e., based on whether the articulating surfaces of the adjacent bones are directly connected by fibrous connective tissue or cartilage, or whether the articulating surfaces contact each other within a fluid-filled joint cavity. These differences serve to divide the joints of the body into three structural classifications.
A fibrous joint is where the adjacent bones are united by fibrous connective...
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Classification of Bones01:18

Classification of Bones

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The bones of the human skeletal system are of varied shapes, sizes, and functions. They can be classified based on their shape and function into four major classes: long bones, short bones, flat bones, and irregular bones. Some classifications include a fifth type, the sesamoid bones, as a separate class, whereas others categorize them under short bones.
Long and Short Bones
The appendicular skeleton, particularly the upper and lower limbs, is primarily made of long and short bones. The...
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Articles linked to this work by shared authors, journal, and citation graph.

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The Reconstructive Pelvic Anatomy classification system : a valid and reliable classification system for pelvic reconstruction.

Bone & joint open·2026
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Coronal alignment parameters of the knee predict osteoarthritis development : a Coronal Plane Alignment of the Knee classification-based analysis using the Multicenter Osteoarthritis Study data.

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Reply to the Letter to the Editor: How Can the Use of Patient-Reported Outcomes Data by Orthopaedic Surgeons Be Improved? A National Qualitative Study.

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Related Experiment Video

Updated: Nov 19, 2025

Anterior Cruciate Ligament Transection and Synovial Fluid Lavage in a Rodent Model to Study Joint Inflammation and Posttraumatic Osteoarthritis
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Anterior Cruciate Ligament Transection and Synovial Fluid Lavage in a Rodent Model to Study Joint Inflammation and Posttraumatic Osteoarthritis

Published on: September 2, 2025

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Coronal Plane Alignment of the Knee (CPAK) classification.

Samuel J MacDessi1,2,3, William Griffiths-Jones1,4, Ian A Harris5,6

  • 1CPAK Research Group, Sydney, Australia.

The Bone & Joint Journal
|February 1, 2021
PubMed
Summary

The Coronal Plane Alignment of the Knee (CPAK) classification aids in predicting knee balance for total knee arthroplasty (TKA). Kinematic alignment (KA) demonstrated superior soft tissue balance compared to mechanical alignment (MA) in specific CPAK types.

Keywords:
Arithmetic HKACPAKConstitutional alignmentCoronal Plane Alignment Knee classificationJoint line obliquityKinematic alignmentKnee alignment

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Area of Science:

  • Orthopedic surgery
  • Biomechanical analysis
  • Radiological assessment

Background:

  • Total knee arthroplasty (TKA) requires precise coronal lower limb alignment for optimal knee balance.
  • Existing alignment methods may not adequately predict or address soft tissue balance preoperatively.
  • A classification system for coronal knee alignment could improve TKA outcomes.

Purpose of the Study:

  • To introduce and describe the Coronal Plane Alignment of the Knee (CPAK) classification.
  • To evaluate the CPAK classification's utility in predicting preoperative soft tissue balance.
  • To compare kinematic alignment (KA) versus mechanical alignment (MA) in TKA within CPAK phenotypes.

Main Methods:

  • Radiological analysis of 500 healthy and 500 osteoarthritic (OA) knees to assess CPAK applicability.
  • CPAK classification based on arithmetic HKA (aHKA) and joint line obliquity (JLO).
  • Intraoperative soft tissue balance comparison in 138 computer-assisted TKAs randomized to KA or MA within CPAK phenotypes.

Main Results:

  • Similar frequency distributions of CPAK types were observed in healthy and OA knees.
  • Common CPAK types included II, I, and V; Types VII, VIII, and IX were rare.
  • Kinematic alignment (KA) achieved significantly better optimal knee balance than mechanical alignment (MA) in CPAK Types I, II, and IV.

Conclusions:

  • The CPAK classification is a practical tool for assessing coronal knee alignment in healthy and arthritic knees.
  • CPAK identifies knee phenotypes that may benefit more from KA for optimizing soft tissue balance.
  • This classification promotes consistency in reporting for future total knee arthroplasty research.